Centrifugal fan having inlet guide baffle



I 5. 1969 w. w. STEPHENSON, JR 3,

CENTRIFUGAL FAN HAVING INLET GUIDE BAFFLE Filed Sept. 29, 1967 INVENTOR. WMLATEPHENSON K Twlvis .1? 525m) RESSURE United States Patent 3,480,202 CENTRIFUGAL FAN HAVING INLET GUIDE BAFFLE William W. Stephenson, In, 184 S. Glengarry Road,

' Birmingham, Mich. 48010 Filed Sept. 29, 1967, Ser. No. 671,820 Int. Cl. F04d 17/16, 29/44 US. Cl. 230-127 1 Claim ABSTRACT OF THE DISCLOSURE SUMMARY This invention relates to centrifugal fans, for example fans mounted inside an enclosure such as in central station air handling units. Such central station units conventionally include a large rectangular plenum chamber (enclosure) containing one or more centrifugal fans, each fan comprising a scroll type housing and a centrifugal fan wheel. When more than one fan is used each wheel is usually mounted on a common shaft extending through the large enclosure to a driving connection with an external motor. In service the fan wheels draw air from the plenum chamber into the fan wheel eye and discharge same through the wheel blades into an outlet formed in the scroll housing.

Such fans are usually belt-driven by constant speed motors through a means of power transmission such as sheaves and V-belts selected to run the fan(s) at a particular speed. The speed requirements are determined from the system on which the unit is to be used in terms of the gas volume to be delivered against the resistance pressure (static pressure) of the system. Through well established industry standards, the performance capability of the fans is measured through laboratory testing. Thus an appropriate fan can be selected from the performance ratings so generated. In the case of fan(s) mounted in a cabinet or enclosure, a particular combination of fan(s) size and cabinet size (i.e. unit size) must be selected to meet the specified requirements. It is apparentthat the broader the volume range covered by a given size, the greater will be the application range of that size.

One object of this invention is to broaden the volume range through which fan and/or central station unit can be applied with a minimum reduction in peak static pressure. A further object is to stabilize the operation of the fan(s) throughout the full application range. Through the addition of a novel inlet battle in the eye of the fan inlet of an otherwise conventional centrifugal fan, both of these stated objectives are met.

THE DRAWINGS FIG. 1 is a side elevational view of a centrifugal fan constructed according to the invention.

FIG. 2 is a sectional view taken on line 22 in FIG. 1.

FIG. 3 is a side elevational view of a second centrifugal fan incorporating features of the invention.

FIG. 4 is a fragmentary sectional view taken on line 4-4 in FIG. 3.

FIG. 5 is a chart showing the performance of either the FIG. 1 or FIG. 3 fan compared with a similar prior art fan.

ice

THE DRAWINGS IN GREATER DETAIL The centrifugal fan of FIGS. 1 and 2 comprises a scroll type housing 10 which includes two flat inlet side sheets 12 and 14, and a curved scroll-forming sheet 16. Formed in each side sheet is a circular gas inlet Opening 18 or 20 for admitting gas to the interior of a conventional fan Wheel 22. Gas discharged from the wheel flows past a full width cut-01f sheet 24 and through a rectangular outlet opening 26.

In the illustrated arrangement fan wheel 22 comprises a center plate (or back plate on single inlet fans) 28 suitably secured to a hub 30, said hub being in turn affixed to a rotary shaft 32. At this point it should be noted that conventional central station air handling units (with which the illustrated fan is intended to be used) comprise large rectangular plenum chambers arranged in line with respect to the air treating components, such as the air mixing boxes, filters, heating coils, and/or cooling coils. One or more fans of the type shown in FIGS. 1 and 2 are arranged in the plenum so that air flows into the plenum and thence through each inlet opening 18 or 20.

The fan shaft 32 extends transversely across the plenum chamber. Driving power for the fan or fans is provided by an electric motor having a belt-drive connection with shaft 32. If two or more fans are used they are disposed on a single shaft 32. Each fan is mounted such that discharge opening 26 is essentially in the plane of the exit wall.

The fan wheel 22 is constructed to include a number of forwardly curved blades 34, as for example forty, extending axially from center plate 28 to rigid connections with annular rims 36 and 38. It will be seen therefore that rotation of shaft 32 will produce rotation of blades 34 and movement of gas from inlets 18 and 20 through outlet opening 26. As thus far described, the fan structure and operation are conventional.

The present invention adds to the art in providing circular disc-like bafiles 40 and 42 of optimum diameter, and preferably located in the plane of the inlet side sheets 12 and 14. As shown in FIGS. 1 and 2, each baffle is secured to shaft 32, as by forming one or more flanges 44 on the baflle, and clamping the baflle to the shaft, as by means of a conventional split-sleeve type hose clamp 46. The baflles may be split into two semi-circular sections for ease of assembly to shaft 32. The mechanism for mounting the bafile on shaft 32 should be of such construction as will permit axial adjustment of the baffle along the shaft surface, since the performance depends to a large extent on the axial location.

Test results confirm that the bafiles produce beneficial results when used in central station fans on both single fan and double fan units. FIG. 5 shows the fan volume (CFM) vs. system resistance (SP) curves produced by a fan without the bafiles and by the same fan with the bafiles of FIGS. 1 and 2. Curve 48 represents the fan without the bafile, and curve 50 represents the same fan with the bafile. It will be noted that when the baffle is used, the maximum CFM (at zero resistance) is greater than when the baffle is not used, comparing points 52 and 54. Also the peak pressure point 56 for the bafileequipped fan occurs at a lower CFM than the peak pressure point 58 for the conventional fan. Thus the CFM span for the baflled fan (distance between points 52 and 56 on the volume axis) is greater than the corresponding span for the conventional fan (correseponding distance between points 54 and 58). Further, this is accomplished with only a slight decrease in peak pressure (vertical distance between points 56 and 58).

Since good engineering practice calls for selection of a fan from the peak of the static pressure curve to the right with increasing volume, the broader span exhibited by curve #50 (FIG. 5) using the baffle provides a greater useful CFM span. This increased-span permits greater application of a given size and in some cases permits use of a smaller size than would otherwise be required.

It will be noted that the contour of curve #50 is unlike the results obtained from the usual gas flow restriction, where test points run at the same speed simply reduce in both CFM and SP along system curves, which establishes a new SP curve lower and approximately parallel to the first. Rather, the effect of this inlet baflie is to change the air pattern entering the fan so as to guide the air more uniformly onto the blades and in so doing direct a portion of the air onto the outermost edge of the blades (closest to the housing side sheet 12 or 14). The result is a new static pressure curve of a completely different character reaching its peak pressure sooner and producing a greater air volume in the lowest pressure range.

The invention can be practiced by other bafile structures than shown in FIG. 2. Thus, as shown in FIGS. 3 and 4 the bafi le can comprise a circular disc 60 welded or otherwise secured to a plurality of outwardly radiating sheet metal arms 62, 64 and 66, each of said arms having an out-turned tab or foot portion 68 for securement to the 4 side sheet of the fan housing.

Preferably disc 60 is of annular construction so that it completely surrounds the fan shaft with a running clearance therebetween. The clearance can have a reasonable tolerance since a slight quantity of air can be allowed to flow through the space between the shaft and disc without materially changing the static pressure curve. Test results show the performance of the FIG. 3 construction to be approximately the same as that of the FIG. 1 construction. Other than the construction of the baffle (fixed as opposed to rotating), the fan of FIGS. 3 and 4 is the same as the fan of FIGS. 1 and 2.

It should be noted that best performance to date is attained when the baflle disc is located in the plane of the housing side sheet. Experiments with the baffle displaced outwardly or inwardly of the plane of the side sheet show that the performance CFM span and maximum CFM suffer. Further, the diameter of the bafile also was found to be important. A slight change in baffle diameter caused a substantial change in the static pressure curve with the sizes tested.

The drawings show double inlet fans, but the invention can be practiced with single inlet fans since the theory of operation is the same. It is also believed that the invention can be practiced with fan wheels other than the illustrated forwardly curved type, as for example air foil or backwardly inclined types.

It is claimed:

1. A centrifugal fan comprising a scroll type housing which includes first and second side sheets and an interconnecting scroll-forming wall; one of said side sheets having a circular unobstructed gas inlet opening therein; a fan shaft extending into the housing along the axis of the inlet opening; a centrifugal fan wheel disposed on the shaft within the fan housing; said wheel comprising a back plate, blades extending axially from the plate periphery, and a rim interconnecting the blade ends adjacent said one housing side sheet; and bafile means surrounding the fan shaft to direct gas flow substantially uniformly along the blade length measured from the back plate to the rim; said baffie means comprising a circular disc concentric with and surrounding the shaft, said disc being formed as a flat sheet material element located substantially in the plane of said one housing side sheet having said circular gas inlet; the diameter of said disc being approximately one-half that of the inlet opening; and the space between the baffle sheet and rim being devoid of structure.

References Cited UNITED STATES PATENTS 978,397 12/1910 Rice 230128 2,305,136 12/1942 Campbell 230-127 2,482,847 9/1949 Gooman 230-117 2,661,894 12/1953 Stevenson et al. 230128 2,722,464 11/1955 Galaba 230-128 2,808,981 10/1957 Levy 230235 3,231,176 1/1966 Bowen 230-417 HENRY F. RADUAZO, Primary Examiner US. Cl. X.R. 

